1. Field of the Invention
The present invention relates to media, methods, and apparatuses for recording and reproducing information by means of light irradiation respectively.
2. Description of Related Art
The most significant features of optical disks are removability from their recording/reproducing apparatuses and availability with low prices. Optical disk drives that use those disks are therefore configured so as to enable fast and high density recording without losing such the features of the optical disks.
So far, various well-known principles have been employed for those optical disks; each records information in its recording layer by irradiating a light therein. One of such the principles makes good use of changes of atomic configuration caused by a thermal process, that is, phase-changes of a subject film material (the phase-change is also referred to as phase transition or phase transformation) to enable the information recording medium made of the material to be rewritten many times. For example, a phase-change optical disk disclosed by JP-A No. 344807/2001 is basically configured by a protective layer, a recording film made of a GeSbTe material, a protective layer, and a reflection layer, which are formed sequentially on a substrate.
On the other hand, there are also other well-known optical disks referred to as electric-field-effect type disks. In the case of this type disk, a laser beam is irradiated to its phase-change recording film while an electric field is applied thereto so as to record information therein. This type disk has an element structure in which a phase-change recording layer made of a GeSbTe material or the like is disposed between upper and lower electrodes. This electric-field-effect type optical disk is disclosed, for example, by JP-A No.122032/1988. This type optical disk receives an electric-field in its recording film, thereby the phase-change in the recording film is promoted (crystallization) more than other optical disks for each of which only a laser beam is irradiated to its recording film. FIG. 1 shows a configuration of such an electric-field-effect optical disk. A light 9 is condensed by a lens 8. The disk has electrodes and layers formed on a substrate 7 sequentially from the light incidence side in order of a transparent electrode 1, a UV-resin guide groove layer 2, a recording film 3, an insulator electrode 4, an AI electrode 5, and a protective layer 6. A voltage is applied to both of the transparent electrode and the AI electrode. The UV-resin layer 2 that has a guide groove on its surface is an insulator whose specific resistance is 106 Ω·cm. The UV-resin layer 2 functions as an electric-field-effect and to form the guide groove.
A paper written by the present inventor et al (M. Terao, H. Yamamoto and E. Maruyama) and entitled as “Highly Sensitive Amorphous Optical Memory: supplement to the J. of the Japan Society of Applied Physics Vol. 42, pp 233-238” reports an experimental result that light irradiation to both of a photo-conductor and a phase-change recording film disposed between transparent electrodes while a voltage is applied to them from those transparent electrodes makes it possible to record information in the recording layer only with a laser beam that is weaker by almost two digits than any case in which only a light is irradiated thereto. On the other hand, there are also still other type optical disks like CR-R and DVD-R, each of which uses an organic-material for its recording layer. In the case of those optical disks, a laser beam is irradiated to both of a recording layer and a substrate surface adjacent to the recording layer. The recording layer includes a dye to absorb the wavelength of the recording laser, thereby the quality of the substrate surface is changed to enable information to be recorded therein.
As described above, while optical disks are all characterized by removability from their recording units, as well as availability at low prices realized by using plastic substrates, rapid operation is one of the indispensable requirements for them. And, because of such the structure, optical disks have been confronted unavoidably with problems; each of those disks repeats pitching, resulting in tracking offsets sometimes when it rotates faster. And, this comes to generate a high frequency that makes it difficult for the disk to follow up with auto-focusing and tracking. This is why the recording media have long been required to be permissive to such the tracking offset, especially when in recording during which such the trouble is apt to occur. And, this conventional problem has to be solved to speed up the operation of the recording apparatus to enable such the following-up over the mechanical vibration limit of the apparatus.
According to the technique disclosed in the above-described paper “supplement to the J. of the Japan Society of Applied Physics Vol.42” written by the present inventor et al, as well as the electric-field-effect type recording medium disclosed by JP-A No. 122032/1988, it never occurs that only one of the land area and the groove area becomes easier to be recorded, since almost the same voltage is applied to both of the areas and almost the same light absorption occurs in them. Consequently, the media in the above cases are not permissive so much to the tracking offset and accordingly they cannot cope with fast recording satisfactorily. On the other hand, in the case of the CD-R and the DVD-R, light absorption makes no difference practically between the land area and the groove area, so that no electric current application can assist the recording.
Under such circumstances, it is an object of the present invention to solve the above-described conventional problems and enable mass of information to be recorded stably and rapidly.